Where can i service my Maruti Suzuki carin Mumbai without waiting for an appointment.

If this is an in warranty service, u r best off going to an authorised dealer, & chances r that it is more likely that they have a queue. If course, if ur car is not covered by warranty, u can go to any road side workshop. Again, this depends on which model u have. With M800, & Zen, u can be assured that u will be get a reasonable service, provided u select a good place & get a skilled mechanic to work on ur car.
With newer cars, SX4, estillo, etc, u may be better fof sticking to A.S.S.